The invention relates generally to the field of magnetic bubble technology (MBT) and, more particularly, to means for propagating or transmitting magnetic bubbles, especially in field-accessed mutually exclusive propagation channels.
MBT involves the creation and manipulation of magnetic bubbles in specially prepared magnetic materials. The word "bubble", used throughout this text is intended to encompass any single-walled magnetic domain, defined as a domain having an outer boundary which closes on itself. The application of a static, uniform magnetic bias field orthogonal to a sheet of magnetic material having suitable uniaxial anisotropy causes the normally random serpentine pattern of magnetic domains to shrink into isolated, short cylindrical configurations or bubbles whose common polarity is opposite that of the bias field. The bubbles repell each other and can be moved or propagated by a magnetic field in the plane of the sheet.
Many schemes exist for propagating bubbles along predetermined channels. These techniques can be classed generally as conductor-accessed and field-accessed. In conductor-accessed propagation systems, electrically pulsed conductive loops are disposed in series over the magnetic sheet. In field-accessed propagation systems electrical conductors are not disposed on the magnetic sheet for propagation; instead, an overlay pattern of ferromagnetic elements establishes a bubble propagation channel in which a sequence of attracting poles is caused to be formed in the presence of a continuous, uniformly rotating magnetic drive field in the plane of the sheet.
A major distinctiOn in function between conductor-accessed and field-accessed circuits is that several conductor-accessed circuits can be disposed on the same sheet or "bubble chip" and operated completely separately and exclusively from each other while field-accessed circuits on the same chip all operate at the same time under the control of an ubiquitous uniformly rotating, common drive field.
One attempt at providing field-accessed channel selection is shown in U.S. Pat. No. 3,543,252 to Perneski illustrating several variations on the familiar T-bar circuit to which different permutations of pulsed orthogonal drive fields are applied.
MBT can be used in data processing because magnetic bubbles can be propagated through channels, whether field-acessed or conductor-accessed, at a precisely determined rate so that uniform data streams of bubbles are possible in which the presence or absence of a bubble at a particular position within the stream indicates a binary "1" or "0". Because of its potential for low cost, low power consumption and extremely high bit density, MBT is under active consideration for use in large scale memories of moderate speed. One of the prime design elements of many memory systems utilizing field-accessed magnetic bubbles is the provision of a closed loop bubble path which can be used as a recirculating "shift register". Many memory arrangements of this type employ a plurality of "minor" loops selectively interconnectible with a "major" loop such that bubbles can be transferred between the major and minor loops on command.
The ability to propagate bubbles in one or more recirculating loops without operating other loops on the same chip has until recently been confined to systems employing conductor-accessed circuits. Mutually exclusive closed loop field-accessed bubble propagation circuits are disclosed in copending application Ser. No. 432,450, now U.S. Pat. No. 4,021,790 by Howard H. Aiken, Paul T. Bailey and Robert C. Minnick, entitled "Mutually Exclusive Magnetic Bubble Propagation Circuits" filed Jan. 11, 1974. Discrete mutually exclusive circuit elements and systems composed of them are disclosed in copending application Ser. No. 448,649, now U.S. Pat. No. 3,879,716 by Paul T. Bailey and L. John Doerr III, entitled "Mutually Exclusive Magnetic Bubble Propagation Circuits With Discrete Elements", filed Mar. 6, 1974. Bubble paths having rectangular and parallelogram geometries are disclosed in copending application Ser. No. 455,275, U.S. Pat. No. 3,940,751 by Robert M. Sandfort, entitled "Mutually Exclusive Parallel-Sided Bubble Circuits", filed Mar. 27, 1974. These three copending applications are assigned to the assignee of this application and incorporated herein by reference.
In bubble circuit design, the need often arises for controllably transferring bubbles on one path to another path, for example, from a minor to a major loop in a memory organization. One transfer technique in field-accessed systems is to employ one or more conductor loops which can be pulsed on command to attract bubbles on one path to an alternate path. Another approach to bubble transfer involves the use of conductors plus special field-accessed transfer elements. See, for example, Smith et al, "Dollar Sign Transfer for Magnetic Bubbles" (Paper No. 13.2), 1973 Intermag Conference; U.S. Pat. No. 3,714,639 to Kish et al, and U.S. Pat. Nos. 3,613,058, 3,618,054 and 3,713,116 to Bonyhard et al; and Bosch et al, "1024 - bit Bubble Memory Chip" (Paper No. 26.2), 1973 Intermag Conference. Of course, if conductors are involved at all, the overlay pattern becomes more difficult to implement.
Specific field-accessed transfer systems have been previously described. In Michaelis et al "Magnetic Bubble Repertory Dialer Memory", IEEE Trans. Mag., September 1971, p. 737, minor/major loop transfer "gates" are described which can be simultaneously activated by reverse rotation of the drive field. Distinct T-bar loops are joined by specially designed transfer elements. Propagation on the major and minor loops cannot be reversed without transfering bubbles. Bonyhard et al, "Applications of Bubble Devices", IEEE Trans. Mag., MAG-6, No. 3, Sept. 1970, p. 447 (FIG. 1), also discusses "reverse propagation transfer". The Bonyhard article also describes a different field-accessed transfer gate using magnetically "hard" transfer elements and special drive field pulses for transfer.
Segments of two circuit elements have been joined together before. For example, adjacent T-bar channels often utilize double-T or I-bar configurations, as shown in the Michaelis article, supra, and elsewhere. U.S. Pat. No. 3,713,119 to Bobeck describes a particular circuit which represents a modification of T-bar and Y-bar circuit elements and has common segments pairing the elements.